System for automatically extracting and analyzing residual solvents in material samples

ABSTRACT

A system for quickly and automatically extracting and analysing residual solvents is realised for operating directly in the premises where the packing materials are being manufactured, printed and/or laminated. 
     The system provides for a single unit equipped with a display and a keyboard, and comprises an extraction (desorption) chamber ( 1 ), an analysis chamber with valves and separating columns, a detection system ( 17 ), and a data processing system ( 19 ). 
     The extracting or desorption chamber comprises a desorption cell ( 1 ) for receiving a vial ( 36; 37 ) containing said sample, and means are provided to keep the inside of said cell ( 1 ) at a pressure higher that that of the surrounding environment until a new sample has been introduced into the cell, thus accomplishing a “washing” of cell for eliminating polluting solvents coming from the desorption of a preceding sample and/or solvents present in the surrounding environment.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a system for quickly and automaticallyextracting and analysing residual solvents in material samples.Hereinbelow reference will be made particularly to preferred embodimentsof the invention in which the samples are printed and/or laminatedfilms, in general used as base supports for packing or packagingfoodstuffs or pharmaceutical products, or liquid samples. Nevertheless,this is not to be understood as a limitation since the invention hasseveral different applications, such as the analysis of residualmonomers in polymers, the analysis of contaminated grounds, waters, andso on.

More particularly, the invention can be advantageously employed directlyin the premises or plants where the materials for packing foodstuff andpharmaceutical products are being manufactured or printed and/orlaminated.

As it is known the analyses of residual solvents present in printedand/or laminated packing materials, particularly those for packingfoodstuffs and pharmaceutical products, are very important for thecompanies of this field.

According to a prior art technique, the analysis of residual solvents,for example in a film of plastic material, is carried out inlaboratories by using an analytical system comprising a head-spacesample container or thermal desorber, coupled to a gas chromatograph.During the manufacturing of the printed and/or laminated support or atthe end of such process, a sample is collected and sent to thelaboratory. The analysis results from the laboratory are available aftertimes that are not compatible with the manufacturing schedules. Besidesthe high costs, the non-availability in real time of the analysisresults often brings to discard large amounts of product and toreprocess the materials with additional costs.

This analysis is quite complex and requires high qualified technicalpersonnel, and further has the following drawbacks:

-   the handling of the samples from the manufacturing plant to the    analysis laboratory,-   the use of test tubes, envelopes or other closed containers for    transferring the samples to the laboratory with the associated risks    of polluting the container content by the environment air, for    example the air of the manufacturing plant when collecting the    sample;-   extremely complicated calibration procedures and frequent    calibration controls, particularly for systems carrying out a    subdivision or splattering of the sample;-   long analysis times of the order of 45–60 minutes.

A further trouble of the known systems comes from the need to provide apressure source and a gauge, which nevertheless does not allow a realknowledge of the pressure inside of the desorption chamber.

The scope of this invention is to eliminate the drawbacks and thelimitations of the known systems, and more particularly to maintaining ahigher pressure (overpressure) inside the desorption cell until a sampleis introduced thereinto. By providing such overpressure or “washing” ofthe cell, it is possible to eliminate any pollutants coming from thedesorption of a preceding sample and/or from the surroundingenvironment, whereby the system is suitable to be employed in the fieldstill supplying reliable results. Preferably, the same fluid is usedboth as washing fluid and as fluid maintaining the high pressure,although this is not mandatory.

The above objects of this invention are achieved through a novelanalyser for quickly analysing the residual solvent of a sample whichanalyser can be directly used in the sites where the packing article isbeing manufactured, printed and/or laminated.

The analyser according to the invention operates in a fully automaticmanner and does not require highly trained personnel, reduces thehandling of the samples to be analysed, and supplies results that arecomparable with those obtainable in a laboratory by using the knownprocedures in times of the order of several minutes.

More particularly, for analysing printed and/or laminated packingarticles, the system according to the invention can be advantageouslylocated in the manufacturing premises, thus allowing for both theon-line analysing and the monitoring of the article being manufactured.As for what concerns the samples of packing materials, the inventionallows to obtain the automatic analysis of solvent on both the sides ofthe sample, that is both on the outer side and on the inner side (thatcontacts the foodstuff or pharmaceutical product).

Moreover, the system according to the invention can operate on verysmall amounts of sample (the term “sample” being referred to the amountof the residual solvent) directly in the capillary column, thuseliminating sample splitting techniques that are subjected to introduceerrors in the analysis.

According to the invention, these objects are achieved through a systemfor automatically extracting and analysing residual solvents inmaterials samples as described here.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be disclosed with particular reference to theattached drawings illustrating a non limiting embodiment thereof, inwhich:

FIG. 1 is a schematic perspective view of an equipment implementing thesystem according to the invention;

FIG. 2 is a general diagram of a system according to the invention;

FIG. 2A schematically illustrates some steps of the method according tothe invention;

FIG. 3 is a cross section view illustrating with more details thedesorption cell for a liquid or solid sample;

FIG. 4 is a cross section view illustrating with more details thedesorption cell for a film or a support of packing materials;

FIG. 5 shows an analysis diagram obtained by a system according to theinvention;

FIG. 6 schematically illustrates a preferred embodiment for realisingsome of the system valves through a single small volume automatic valveassembly.

Throughout all the Figures the same numerical references have been usedto indicate equal or substantially similar parts.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a system according to the inventionpreferably comprises a single equipment piece disposed inside acontainer or thermostatic case 50, housing an analysis chamber equippedwith valves and a separation column, and a data processing system. Onthe front panel of the equipment there are mounted an analysing ordesorption cell 1, preferably kept at a fixed temperature, and a graphicdisplay 52. A keyboard 51 for the controls is connected to theequipment, as well as a printer (not shown) to supply a hard copy of theanalysis results.

The diagram of FIG. 2 illustrates with more details the components andthe system operation. Such a system comprises a desorption cell 1 forextracting the solvents from a sample, that can be connected to a highresolution capillary column 16 in order to separate from one another thesolvents present in the sample to be analysed. The column 16 isconnected to a detection system 17, to a sampling loop 9, and to aprocessing and control unit 19. These components (as well as their modesof use) are known and however their functions could also be performed bydifferent components so that they shall not be further described.

Additionally, means (not illustrated in the drawings) are provided forheating the sample and extract the solvents. Several fittings areprovided for in the system for connecting this latter to the outside,such as:

-   a fitting 20 to be connected to a vacuum source;-   a fitting 21 to be connected to a source of washing gas;-   a fitting 22 for discharging the washing gas outside of the    apparatus;-   a fitting 23 to be connected to a pressure source;-   a fitting 24 to be connected to a reference standard;-   a fitting 26 for discharging the loop.

Moreover, a digital device 13 for controlling the vacuum level can beconnected to the fitting 20, this device acting on a valve 14 (or othercomponent) for adjusting the vacuum level, such valve being inserted inthe connection between the fitting 20 and the vacuum source.

The fittings 20, 22, 23, 24 and 25 can be connected to the cell 1through the corresponding valves 2, 4, 5, 6 and 7. The inlet of column16 is connected to the fitting 26 through the valve 11, and to one endof loop 9 through the valve 8. The other end of loop 9 is connected tofitting 25 through a valve 10, to fitting 21 through a valve 3, and tofitting 26 through a valve 12.

A device 15 for controlling and adjusting the pressure is locatedbetween valves 7 and 8.

The cycle phases, the switching of the valves as well as otheroperations such as integrations, display of the chromatogram, datastorage and so on, are under the control of unit 19, preferably realisedthrough a PC located inside the analyser.

Valves 2 to 6 are preferably realised as a monolithic (single) componentcomprising a single automatic valve assembly of small volume,schematically illustrated in FIG. 6, adapted to accomplish the requiredfunctions and installed into a thermostat system.

The valve 7, 8, 10, 11 and 12 realise an automatic valve assemblyadapted to directly sample volumes from the capillary column and capableto sample a few microliters of sample without requiring specialsplitting techniques of the sample, thus eliminating the analysis errorsinherent to such techniques.

With reference to FIG. 3 it will be illustrated an embodiment of adesorption cell which is adapted to be used with solid or liquidsamples. Said desorption cell comprises a recess or seat 31 having asubstantially cylindrical shape, formed in a properly insulated portion32 of the equipment front panel and of a closing member or knob, 33 forsealingly closing the cell. A conduit 35, connected to the abovementioned valve 4 of the washing fitting 21 opens into the front portionof the cell and a needle 34 is located at the inner end of the cell.

The cell or seat 31 can receive test tubes or “vials” having a 20 cccapacity, said vials being either vials of the open type such as 37 orvials 36 for liquid or solid samples, that have been sealed through aring carrying a pierceable septum. The thickness of the test tube orvial is such as the inner available volume of the cell is of 20 cc afterthe tube has been inserted into the seat.

After the introduction into the cell of a test tube closed by a septum35, the closing knob 33 is screwed and sealingly tightened onto the testtube till the needle 34 perforates the septum.

FIG. 4 illustrates a cell adapted for analysing residual solvents inbases of printed and/or laminated packing for foodstuffs andpharmaceutical products, both on the outer and the inner surface of thepacking sheet, this latter being the surface that will come in contactwith the packed product. The cell comprises a recess divided by a net 43for supporting the sample to be analysed, and forming two hollows 41 and42, each one with a 20 cc volume. The recess is placed in an insulatedvolume 40 and the seal is ensured by at least one circular gaskets 412fitting along the whole surface of hollow 42. Two conduits 46 and 47 forthe connection to the washing and vacuum sources respectively, as wellas two conduits 45 and 44 for the outlet of the vapour solvent, open inthe hollows 41 and 42. Clamps 48 and 49 lock the cell into the correctposition.

An analysis cycle of a system according to the invention will now bedisclosed in detail.

Initially, a calibration cycle is carried out—wherein the desorption isnot activated—by inserting into the desorption cell a mixture having aknown concentration, such mixture being inserted either through a testtube or a vial closed by a pierceable septum, or by injecting thecalibration mixture directly into the cell 1 by means of a syringe,through a pierceable septum.

A check of the calibration stability in the time can be carried out byusing a reference standard by connecting to the fitting 24 a cylindercontaining synthetic air with a known concentration of only onesubstance, such as for example methane. The reference calibration cycleis comparable with the cycle for analysing the sample and provides for afirst analysis to store the value of methane area, and then a comparisonof such value with a value that has been stored in subsequent referencecalibration cycles.

For the real analysis, from an initial condition of standby, the valves3, 7 and 4 are opened, whereby the desorption cell and the samplingloop, as well as the valve 11 for conveying a gas or “carrier” to thecapillary column, are subjected to a washing.

Then the operator introduces the sample into the chamber 1 and startsthe system, thus causing the closing the previously opened valves 3, 7and 4, and the opening of valves 2 and 7 that apply the vacuum to thecell 1, to the loop 9 and to the valve 11, according to a predeterminedcycle for a duration of a few minutes. During this cycle, the partialpressure is measured and monitored by the device 15 for controlling andadjusting the pressure.

The control of the partial pressure value inside the chamber during thesample desorption phase is very advantageous since it supplies anindication of the quantity of solvent desorbed (i.e. extracted) fromsample. Of course, the value of such partial pressure shall beproportional to the amount of the desorbed solvent. Moreover thiscontrol allows for a later validation of the analysis results byverifying that the partial pressure value has always remained under thepreset pressure value for the sample pressurization cycle.

Once the solvent desorption has occurred, that is when the solventpresent in the sample has been converted to a gas in the cell, the valve7 is opened again for communicating the sampling loop with thedesorption cell 1 and the valve 11 with the capillary column.

The gaseous sample is therefore pressurised by opening the valves 5 and7, respectively towards the pressurisation fitting 23 and the discharge25 fitting, and the valve 11 of carrier to the capillary column. Throughthis pressurisation cycle a sufficient amount of gaseous sample toperform the analysis is achieved.

Then, the valves 7 and 10 are open to fill the loop with the gaseoussample and to bring the loop of the gaseous sample to the atmosphericpressure. Thereafter the valve 11 of the carrier is opened to thecapillary column.

Then the gaseous sample is admitted into the gas chromatography column16. By opening the valves 12 and 8 the carrier draws the gaseous samplefrom the sampling loop and introduces it into the analysis column. Byusing a quick capillary column, it is possible to obtain the separationof the solvents and the analysis printout and report in a time of about2 minutes. At the end of the analysis cycle, the system comes back tothe stand-by conditions.

The cycle of the reference standard is carried out after the calibrationcycle and is identical to the analysis cycle but for the opening of thevalve 6 after the sample has been introduced, by introducing the samplewithout the vacuum cycle. The system stores the response signal of thereference standard and checks its reproducibility in the time, bycomparing the data obtained with those stored: as long as this value isreproducible, the system is properly calibrated.

FIG. 2A shows the values P of the pressure in the desorption cell as afunction of time t. The AB section at a pressure p1 higher than theatmospheric pressure corresponds to the washing phase in which the gaskeeps the cell at a pressure higher than the environment pressure toprevent the inlet of polluting solvents deriving either from thedesorption of a previous sample or from the environment air containingsolvents. The analysis starts at time AN.

At the beginning of the operations, the connection with the source ofhigh pressure is closed and the pressure in the cell drops to theatmospheric value (p0) in the CD portion, the cell is then opened andthe sample to be analysed is introduced in the cell. If the test tube isof the closed type, the needle 34 perforates the closing. During thedesorption phase (in which the sample is being heated), the pressure canbe kept either at the atmospheric level (as shown by the DE portion), orto a lower value (as shown by the FG portion) by connecting the chamberto the vacuum source. At the end of the desorption, the pressure israised again to p1 level and the analysis cycle starts.

The valve assembly shown in FIG. 6 comprises a body 55 and a head 57joined by a screw 58 with a diaphragm 59 interposed between the parts.

Although the invention has been illustrated with reference to preferredembodiments, it is generally susceptible of further applications andmodifications that fall within the invention scope as will be evident tothe skilled of the art.

1. A system for automatically extracting and analysing the content ofresidual solvents in solid material samples, comprising: means forheating a sample in order to desorb or extract a solvent and comprisinga desorption cell adapted to receive a vial having an opening at bothends and containing said sample; an analysis chamber with a separationcolumn to separate components to be analysed; a plurality of valves formoving fluids inside said system; a detection system to identify thesolvents; a control unit for controlling said plurality of valves andprocessing data; a casing kept at a predetermined temperature housing apart of said components; wherein said system further comprises a washingfluid source using a determined fluid for washing said cell and saidopen vial, and being connected to a washing valve; a pressure fluidsource using said determined fluid for maintaining said cell and saidopen vial at a pressure higher than the atmospheric pressure, and beingconnected to a pressure valve; a vacuum source for maintaining said celland said open vial at a pressure lower than the atmospheric pressure,and being connected to a vacuum valve; a pressure control deviceconnected to said washing fluid source, to said pressure fluid sourceand to said vacuum source through the respective valves and configuredfor measuring, monitoring, and controlling the pressure inside said celland said open vial; said pressure control device being arranged formeasuring, monitoring, and controlling inside said cell at least threepressure levels: a pressure higher than the atmospheric pressure to washsaid cell and said vial, and prevent the admission into said cell andsaid open vial of solvents from the surrounding environment; a pressuresubstantially equal to the atmospheric pressure to introduce the samplein the open vial and in the cell; a pressure lower than the atmosphericpressure to desorb said solid material samples; said control unit beingarranged for controlling opening and closing of said respective washingvalve, pressure valve and vacuum valve.
 2. A system as claimed in claim1, further comprising a one-piece valve assembly incorporating at leastsaid pressure valve and said vacuum valve.
 3. A system as claimed inclaim 1, wherein said control unit is configured for maintaining saiddesorption cell a predetermined temperature.
 4. A system as claimed inclaim 1, wherein said analysis chamber comprises a capillary columnadapted to separate the solvents present in the sample to be analysed,the capillary column being connected to a detection system, to asampling loop, and to said control unit, and to a plurality of fittingsfor the outside connections including a fitting to be connected to avacuum source, a fitting to be connected to said washing fluid source, adischarge fitting for the washing fluid, a fitting to be connected tosaid pressure fluid source, a fitting for a reference standard, and aloop discharge fitting.
 5. A system as claimed in claim 1, furthercomprising a keyboard.
 6. A system for automatically extracting andanalysing the content of residual solvents in solid material samples,comprising: means for heating a sample in order to desorb or extract asolvent and comprising a desorption cell for containing said sample; ananalysis chamber with a separation column to separate components to beanalysed; a detection system to identify the solvents; a plurality ofvalves for moving fluids inside said system; a control unit forcontrolling said plurality of valves and processing data; a casing keptat a predetermined temperature housing a part of said components;wherein said cell comprises a recess having two hollows of equal volumesand being placed in a thermally insulated space, and a net interposedbetween said two hollows for supporting the sample to be analysed, saidhollows comprising respective outlet conduits connected to said analysischamber for the outlet of the desorbed sample, and respective inletconduits connected to inlet conduits for washing said cell and forreducing the pressure therein, said cell allowing the analysis ofresidual solvents in printed or laminated packing materials for packingor packaging foodstuffs and pharmaceutical products, both on the outerside and on the inner side in contact with the packed article.
 7. Asystem as claimed in claim 6 further comprising a sealing circulargasket inserted along the whole surface of one of said hollows.